The invention relates to a method for operating a hybrid vehicle comprising an internal combustion engine and an exhaust after treatment device for treating exhaust gases from the engine. The invention further relates to a computer program, a computer readable medium, a control unit, a hybrid vehicle propulsion system and hybrid vehicle.
The invention can be applied in heavy-duty vehicles, such as trucks, buses and construction equipment. Although the invention will be described with respect to a bus, the invention is not restricted to this particular vehicle, but may also be used in other vehicles such as cars.
In a hybrid electric vehicle there is an aim to keep emissions from the internal combustion engine as low as possible. A further aim is to control the propulsion system for an optimal energy use efficiency in view of the operational circumstances. Thereby, the engine may be turned off or operating a low load during extensive time periods or during time periods occurring at high frequencies. As a result the temperature of an exhaust after treatment device of the engine, such as a selective catalytic reduction (SCR) unit, may fall below a point at which the device works effectively. This problem may be particularly pronounced in hybrid electric buses or delivery vehicles operating in urban areas.
WO2013188513 discloses a hybrid electric vehicle in which, during an electric mode of the vehicle, the internal combustion engine is turned on in case the catalyst efficient falls below a threshold. However, running the engine for this purpose may compromise said aim to provide an optimal energy use efficiency.
It is desirable to move the operation of a hybrid vehicle closer to an optimal balance between keeping emissions from the internal combustion engine as low as possible, and obtaining a maximum energy use efficiency.
According to an aspect of the invention a method is provided for controlling a hybrid vehicle propulsion system comprising an internal combustion engine and an exhaust after treatment device for treating exhaust gases from the engine, the method comprising
determining during operation of the vehicle a value of a parameter indicative of an efficiency of the exhaust after treatment device,
characterized by
identifying a vehicle operation cycle start event,
determining during the operation of the vehicle an engine operation history characteristic for a time interval after the vehicle operation cycle start event, and
determining whether or not to control the propulsion system so as to increase the efficiency of the exhaust after treatment device, in dependence on the determined exhaust after treatment device efficiency parameter value and the determined engine operation history characteristic.
The exhaust after treatment device may be any such device suitable for the engine type provided. E.g. where the engine is a diesel engine, the exhaust after treatment device may be a selective catalytic reduction (SCR) unit. It should be noted however, that the invention is applicable where the exhaust after treatment device is of another type, in particular of a type requiring a temperature above a minimum temperature for operating fully efficiently.
Determining whether or not to control the propulsion system so as to increase the efficiency of the exhaust after treatment device may comprise determining whether or not to control the engine so as to run. Where said parameter value indicates that the exhaust after treatment device efficiency is low, controlling the engine so as to run may improve the efficiency of the exhaust after treatment device. For example, running the engine may increase the temperature of the exhaust after treatment device, thereby increasing its efficiency. This may contribute to keeping the emissions of the engine as low as possible.
However, identifying the vehicle operation cycle start event, and determining during the operation of the vehicle the engine operation history characteristic for the time interval after the vehicle operation cycle start event provides a strong indication of whether increasing the exhaust after treatment device efficiency is useful during the operational circumstances at the time. E.g. where the engine operation history characteristic indicates that the engine has been shut down since the vehicle operation start event, it may be reasonable to assume that the engine will continue to be shut down for a relatively long time period to come.
For example, where the hybrid vehicle is a hybrid electric vehicle and where the engine has been shut down since the vehicle operation start event, the reason might be that the vehicle is in a prolonged fully electric propulsion mode, in which all propulsion power is provided by an electric motor powered by a battery pack. Thereby, the vehicle operation cycle start event may be an event involving charging of the battery pack from an external power source, e.g. at a charging station. The fully charged battery pack and the operational circumstances may allow the vehicle to be driven in the fully electric propulsion mode for a relatively long time before the engine is needed for propulsion assistance.
If in such a situation, the propulsion system is controlled so as to increase the efficiency of the exhaust after treatment device, this control action may be followed by a further engine shutdown period long enough for the exhaust after treatment device to once again lose efficiency. Therefore, said control action will have had no benefit. For example, if the engine is started to increase the temperature of the exhaust after treatment device, the result may only be that once the exhaust after treatment device has become fully efficient, the engine is shut down for a further extended time period and the exhaust after treatment device temperature will again it so as to render the device less efficient. As a consequence, running the engine will have merely caused an increased fuel consumption and hence a reduced energy use efficiency. In addition, emissions will have increased due to the engine having been running as opposed to having been shut down.
Thus, the engine operation history characteristic may be used as an indication that the engine will remain shut down for yet some time to come, and that running it to increase the exhaust after treatment device efficiency will serve no purpose. Instead the engine may be kept shut down, and turned on later for some other reason such as the engine being needed for supporting the vehicle propulsion. It should be noted that in some embodiments the engine may be turned on for charging the battery pack.
However, where the engine operation history characteristic suggests that the engine has been running to a relatively large extent since the vehicle operation cycle start event, this may indicate that the vehicle is in an operational mode in which the engine is frequently turned on to support the vehicle propulsion. In such a situation it is reasonable to assume that where the engine is turned off, it will be turned on again within a relatively short time period. Therefore, the interest of keeping emissions low will be served by running the engine to increase the temperature of the exhaust after treatment device in order to avoid its efficiency dropping during a time period when the engine is turned off.
Thereby the engine may be controlled so as to run although there is no other control function for the propulsion system, e.g. vehicle propulsion, requesting that the engine is controlled so as to run. Where the increase of the efficiency of the exhaust after treatment device is the only control object causing a request that the engine is controlled so as to run, the engine may be kept at idle during vehicle standstill.
It is understood that said time interval after the vehicle operation cycle start event may be the time from the vehicle operation cycle start event to the time of the determination of the engine operation history characteristic, and/or the determination of the exhaust after treatment device efficiency parameter value. Alternatively, said time interval may start at some point in time after the vehicle operation cycle start event and/or it may end at some point in time before the determination of the engine operation history characteristic and/or the determination of the exhaust after treatment device efficiency parameter value.
It is also understood that the determination whether or not to control the propulsion system so as to increase the efficiency of the exhaust after treatment device may be made regardless whether the engine is turned off or whether it is already running when the determination is made. However, in some embodiments the method may comprise determining during the operation of the vehicle whether or not the engine is running, and, if it is determined that the engine is not running, determining whether or not to control the engine so as be started, in dependence on the determined exhaust after treatment device efficiency parameter value and the determined engine operation history characteristic.
In some embodiments, the control of the propulsion system so as to increase the efficiency of the exhaust after treatment device, may be disabled e.g. where the vehicle is in an “electric zone”, i.e. an area in which regulations prohibit internal combustion engines to be operated. The positioning of the vehicle in such an area may be done e.g. by means of a global positioning system (GPS) device.
The control of the propulsion system so as to increase the efficiency of the exhaust after treatment device may include at least one additional control action other than controlling the engine so as to run. One or more of such additional control actions may be performed in parallel to the control of the engine so as to run. They are particularly beneficial in cases where the engine is started after having been shut down for a relatively long period of time. A cool engine running might actually contribute to decreasing the exhaust after treatment device temperature rather than increasing it. An additional control action so as to increase the efficiency may counteract such an effect of a cool engine.
For example, where the engine is connectable to wheels of a vehicle in which the propulsion system is arranged, via a transmission, the control of the propulsion system so as to increase the efficiency of the exhaust after treatment device may comprise adjusting a gear shift strategy of the transmission. The adjusted gear shift strategy may involve using lower gears at vehicle start from standstill to increase the heat from engine.
An advantageous additional control action so as to increase the efficiency of the exhaust after treatment device may be provided where the hybrid vehicle propulsion system is a hybrid electric vehicle propulsion system comprising an electric motor, wherein the engine and the motor are arranged to deliver in parallel a combined torque to at least one wheel of a vehicle in which the propulsion system is arranged. Such a propulsion system may be referred to as a parallel hybrid vehicle propulsion system. Thereby, the control of the propulsion system so as to increase the efficiency of the exhaust after treatment device may comprise decreasing a portion of the combined torque delivered by the motor. This may involve decreasing the electric motor boost while the engine is engaged in the vehicle propulsion. For example, the allowance of the motor to assist the engine during vehicle acceleration may be limited. The increased engine work may increase the heat produced by the engine so as to increase the temperature of the exhaust after treatment device.
In another additional control action so as to increase the efficiency of the exhaust after treatment device, the control of the propulsion system so as to increase the efficiency of the exhaust after treatment device may comprise control of the engine so as to run in a high heat mode. Such a high heat mode is adapted to quickly heat the engine, the exhaust gases and/or the exhaust after treatment device. The high heat mode may involve an increased fuel flow to the engine, an adjusted, e.g. late, fuel injection timing, an adjusted, e.g. early, exhaust valve opening (where a variable valve timing system is provided), actuation of exhaust gas recirculation (EGR), suitable control of an air intake throttle, and/or suitable control of a variable geometry turbocharger (VGT) of the engine.
In some embodiments, the control of the propulsion system so as to increase the efficiency of the exhaust after treatment device may include only controlling the engine so as to run, without any additional control action as exemplified above.
Determining the engine operation history characteristic for the time interval after the vehicle operation cycle start event may comprise determining an extent to which the engine has been running since the vehicle operation cycle start event, which in turn may comprise determining whether or not the engine has been running at any point in time since the vehicle operation cycle start event. Thus, the determination of the extent to which the engine has been running since the vehicle operation cycle start event may involve determining whether or not the engine has been running for more than zero seconds at least once. Thereby the indication of whether or not increasing the exhaust after treatment device efficiency is useful during the operational circumstances at the time is reinforced.
The engine operation history may be stored in a data storage which is accessible to a control unit for controlling the propulsion system. As an alternative to determining whether or not the engine has been running at any point in time since the vehicle operation cycle start event, determining the engine operation history characteristic may involve determining whether or not the engine has been running continuously for a time exceeding a predetermined time interval threshold.
Preferably, the exhaust after treatment device efficiency parameter is a temperature of the exhaust after treatment device, the method comprising comparing the determined temperature to a threshold temperature which preferably is predetermined. Thereby, a strong indication is given whether the exhaust after treatment device is operating efficiently, e.g. where the device is a selective catalytic reduction (SCR) unit. Alternatively, or in addition, other parameters may be used for determining the efficiency of the exhaust after treatment device, such as the change of the temperature of the exhaust after treatment device, or, where the exhaust after treatment device is an SCR unit, the size of the urea buffer therein.
Preferably, determining whether or not to control the propulsion system so as to increase the efficiency of the exhaust after treatment device, e.g. by controlling the engine so as to run, comprises determining to control the propulsion system so as to increase the efficiency of the exhaust after treatment device if the determined temperature is below the threshold value and if the engine has been running more than to a predetermined extent since the vehicle operation cycle start event. Preferably, determining whether or not to control the propulsion system so as to increase the efficiency of the exhaust after treatment device, e.g. by controlling the engine so as to run, comprises determining to not control the propulsion system so as to increase the efficiency of the exhaust after treatment device if the determined temperature is below the threshold value and if the engine has been running less than to a predetermined extent since the vehicle operation cycle start event. Thereby uselessly, in view of the operational circumstances, increasing the exhaust after treatment device efficiency may be effectively avoided. In some embodiments, such as an embodiment described above, the predetermined extent to which the engine has been running may be that the engine has been running to any extent, regardless of the size of the extent. In such embodiments it may be determined to not control the propulsion system so as to increase the efficiency of the exhaust after treatment device if the determined temperature is below the threshold value and if the engine has not been running since the vehicle operation cycle start event.
After the vehicle operation cycle start event, the engine may be controlled so as to run more than to the predetermined extent based on at least one additional condition, which is not the determined temperature being below the threshold value, and subsequently it may be determined to control the engine so as to run if the determined temperature is below the threshold value.
The additional condition may be e.g., where the system is a parallel hybrid vehicle propulsion system, that a propulsion torque request exceeds the available torque capacity of an electric motor of the propulsion system. The additional condition may alternatively or in addition be that one or more auxiliary devices of the vehicle needs power from the engine. The additional condition may in some embodiments be that a battery pack of the propulsion system needs charging. If the engine is controlled so as to start running due to the additional condition being fulfilled, and subsequently the additional condition is not fulfilled anymore, the engine might be controlled so as to continue running due to the determined exhaust after treatment device temperature being below the threshold value.
As understood from the description above, when the additional condition is fulfilled and the determined temperature is below the threshold value, the control of the propulsion system so as to increase the efficiency of the exhaust after treatment device may include control actions in addition to controlling the engine so as to run, e.g. adjusting a gear shift strategy of the transmission, decreasing a portion of the torque delivered to the wheels by the electric motor, and/or control of the engine so as to run in a high heat mode.
Preferably, the step of determining the engine operation history characteristic is performed substantially simultaneously to the step of determining the exhaust after treatment device efficiency parameter value. This may provide a large degree of correlation between the determined exhaust after treatment device efficiency parameter value and the determined engine operation history characteristic. In turn this may improve the accuracy of the control of the hybrid vehicle propulsion system.
The vehicle operation cycle start event may be a start of a predetermined route of a vehicle provided with the propulsion system. For example, the predetermined route may be a bus route, or a delivery route. A delivery route may be followed e.g. by a truck or a car, for example in a shipping or postal delivery system. Information about the predetermined route may be stored so as to be accessible to a control unit for the propulsion system. In addition, information about the position of the vehicle, e.g. from a global positioning system (GPS) device, may be accessible to the control unit. Upon matching the vehicle position with the origin of the predetermined route, the vehicle operation cycle start event nay be identified.
In addition or alternatively, the predetermined route may be determined by means of a navigation planning device. Such a device may include e.g. a GPS device. The device may be fitted in a car, e.g. for private use. A control unit of the propulsion system may be arranged to receive information from the navigation planning device. Upon a planned route being determined by the navigation planning device, e.g. based on input from a person, the vehicle operation cycle start event may be identified.
In some embodiments, where the hybrid vehicle propulsion system is a hybrid electric vehicle propulsion system comprising an electric motor and an electric energy storage arrangement, e.g. a battery pack, the vehicle operation cycle start event may be charging of the electric energy storage arrangement. Thereby, based on the assumption that after such charging the propulsion system may be able to operate mostly or entirely in a fully electric mode during a relatively long period of time after the charging event, it can be decided that the control of the propulsion system so as to increase the efficiency of the exhaust after treatment device may be omitted even if the exhaust after treatment device efficiency of low, since it can be assumed that the fully electric mode will continue for a further extended time period. Thereby, a useless exhaust after treatment device efficiency increasing action may be omitted.
Where the hybrid vehicle propulsion system is a plug-in hybrid electric vehicle propulsion system comprising an electric motor and an electric energy storage arrangement, identifying the vehicle operation cycle start event may comprise identifying charging of the electric energy storage arrangement from a source externally of the vehicle. A control unit for the propulsion system may be arranged to detect such external charging. Thereby, the vehicle operation cycle start event may be positively and securely identified. Since a plug-in hybrid electric vehicle propulsion system may have a particularly large battery pack, it can be expected that after an external charging event, the vehicle may be operating in a fully electric mode for a relatively long period of time. As understood from the description above, embodiments of the invention will provide for useless exhaust after treatment device efficiency increasing actions being avoided during the fully electric mode of the plug-in hybrid electric vehicle following the external charging event.
In some embodiments, where the hybrid vehicle propulsion system is a hybrid electric vehicle propulsion system comprising an electric motor and an electric energy storage arrangement, identifying the vehicle operation cycle start event comprises identifying a positive change of a state of charge of the electric energy storage arrangement. Such a positive change of the state of charge may signify a charging event, which may be provided by means of an external source. In some embodiments, a positive change of the state of charge may signify an internal charging event in the system, e.g. by means of the engine. Preferably, it is determined whether or not the positive change of the state of charge is above a predetermined threshold value. If the positive change of the state of charge is above the predetermined threshold value, it may be assumed that the charging event is followed by an extended fully electric mode of the vehicle. Thereby, the vehicle operation cycle start event may be positively and securely identified, and useless exhaust after treatment device efficiency increasing actions ma be avoided during the fully electric mode. In alternative embodiments, identifying the vehicle operation cycle start event comprises determining that a state of charge of the electric energy storage arrangement is above a predetermined threshold value.
Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims.